System and method of forming a porous low-k structure

ABSTRACT

The present disclosure involves forming a porous low-k dielectric structure. A plurality of conductive elements is formed over the substrate. The conductive elements are separated from one another by a plurality of openings. A barrier layer is formed over the conductive elements. The barrier layer is formed to cover sidewalls of the openings. A treatment process is performed to the barrier layer. The barrier layer becomes hydrophilic after the treatment process is performed. A dielectric material is formed over the barrier layer after the treatment process has been performed. The dielectric material fills the openings and contains a plurality of porogens.

PRIORITY DATA

The present application is a continuation of U.S. patent applicationSer. No. 16/016,804, filed Jun. 25, 2018, which is a divisionalapplication of U.S. patent application Ser. No. 14/813,177, filed onJul. 30, 2015, entitled “Semiconductor Device Having a Porous Low-KStructure”, which is issued as U.S. Pat. No. 10,008,382 on Jun. 26,2018, the disclosure of which are hereby incorporated by reference intheir entirety.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. Technological advances in IC materials and design have producedgenerations of ICs where each generation has smaller and more complexcircuits than the previous generation. However, these advances haveincreased the complexity of processing and manufacturing ICs and, forthese advances to be realized, similar developments in IC processing andmanufacturing are needed. In the course of integrated circuit evolution,functional density (i.e., the number of interconnected devices per chiparea) has generally increased while geometry size (i.e., the smallestcomponent (or line) that can be created using a fabrication process) hasdecreased.

As a part of the semiconductor fabrication, metal trenches may beformed. The metal trenches may serve as the metal lines that provideinterconnections for the various components for an IC. The metaltrenches are separated by a low-k dielectric material. However,conventional semiconductor fabrication techniques have not provided alow-k dielectric material that is porous enough. This may adverselyaffect the performance of the conventional semiconductor ICs.

Therefore, while the low-k materials in conventional ICs have beengenerally adequate for their intended purposes, they have not beenentirely satisfactory in every aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIGS. 1-5 and 9-12 are diagrammatic cross-sectional side views of asemiconductor device at various stages of fabrication in accordance withsome embodiments of the present disclosure.

FIGS. 6A-6B illustrate chemical formulas of a first component and asecond component of a precursor used in forming a low-k dielectricmaterial in accordance with some embodiments of the present disclosure.

FIG. 7 illustrates diagrams of monomers and a micelle that is made up ofthe monomers in accordance with some embodiments of the presentdisclosure.

FIGS. 8A-8B illustrate chemical formulas of surfactant type porogensthat can form the micelle of FIG. 7 in accordance with some embodimentsof the present disclosure.

FIG. 13 is a graph illustrating the variation of silicon content insidea low-k dielectric material in accordance with some embodiments of thepresent disclosure.

FIG. 14 is a flowchart illustrating a method of fabricating asemiconductor device in accordance with some embodiments of the presentdisclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

As semiconductor fabrication technologies continue to evolve, low-kdielectric materials have been used to provide isolation betweenconductive elements (such as metal trenches) in an integrated circuit(IC). A low-k dielectric material may refer to materials whosedielectric constant is lower than that of silicon dioxide, which isabout 3.9. In other words, low-k dielectric materials have dielectricconstants less than about 3.9. Typically, as the porosity of adielectric material increases, the dielectric material exhibits betterlow-k properties, which is desirable. For example, a more porous low-kstructure may offer better RxC performance. Unfortunately, conventionalsemiconductor fabrication has not been able to provide a dielectricstructure with sufficient porosity. Therefore, the embodiments of thepresent disclosure discussed below relate to a low-k dielectricstructure having increased porosity and a method of fabricating suchlow-k dielectric structure.

FIGS. 1-5 and 9-12 are diagrammatic fragmentary cross-sectional sideviews of a semiconductor device 50 at various stages of fabrication inaccordance with various aspects of the present disclosure. Thesemiconductor device 50 may include an integrated circuit (IC) chip,system on chip (SoC), or portion thereof, and may include variouspassive and active microelectronic devices such as resistors,capacitors, inductors, diodes, metal-oxide semiconductor field effecttransistors (MOSFET), complementary metal-oxide semiconductor (CMOS)transistors, bipolar junction transistors (BJT), laterally diffused MOS(LDMOS) transistors, high power MOS transistors, or other types oftransistors.

Referring to FIG. 2 , a semiconductor device 50 includes a substrate 60.In some embodiments, the substrate 60 is a silicon substrate doped witha p-type dopant such as boron (for example a p-type substrate).Alternatively, the substrate 60 could be another suitable semiconductormaterial. For example, the substrate 60 may be a silicon substrate thatis doped with an n-type dopant such as phosphorous or arsenic (an n-typesubstrate). The substrate 60 could include other elementarysemiconductors such as germanium and diamond. The substrate 60 couldoptionally include a compound semiconductor and/or an alloysemiconductor. Further, the substrate 60 could include an epitaxiallayer (epi layer), may be strained for performance enhancement, and mayinclude a silicon-on-insulator (SOI) structure.

In some embodiments, the substrate 60 is substantially conductive orsemi-conductive. The electrical resistance may be less than about 10³ohm-meter. In some embodiments, the substrate 60 contains metal, metalalloy, or metal nitride/sulfide/selenide/oxide/silicide with the formulaMXa, where M is a metal, and X is N, S, Se, O, Si, and where “a” is in arange from about 0.4 to 2.5. For example, the substrate 60 may containTi, Al, Co, Ru, TiN, WN2, or TaN.

In some other embodiments, the substrate 60 contains a dielectricmaterial with a dielectric constant in a range from about 1 to about 40.In some other embodiments, the substrate 60 contains Si, metal oxide, ormetal nitride, where the formula is MXb, wherein M is a metal or Si, andX is N or O, and wherein “b” is in a range from about 0.4 to 2.5. Forexample, the substrate 60 may contain SiO₂, silicon nitride, aluminumoxide, hafnium oxide, or lanthanum oxide.

It is understood that a plurality of drains/sources may be formed in thesubstrate 60, and a plurality of gates may be formed over the substrate60. For reasons of simplicity, however, these drains/sources or gatesare not specifically illustrated herein.

An etching-stop layer 80 is then formed over the substrate 60. Theetching-stop 80 may be formed using a deposition process. In variousembodiments, the etching-stop layer 80 may contain a suitable conductivematerial, such as a metal material.

A conductive layer 90 is then formed over the etching-stop layer 80. Theconductive layer 90 may be formed by a deposition process. In variousembodiments, the conductive layer 90 may contain copper, aluminum,tungsten, or combinations thereof. The material compositions for theconductive layer 90 and the etching-stop layer 80 are configured suchthat there is sufficient etching selectivity between the conductivelayer 90 and the etching-stop layer 80. In other words, the conductivelayer 90 and the etching-stop layer 80 have substantially differentetching rates such that the conductive layer 90 may be etched withoutetching the etching-stop layer 80, or vice versa.

Referring now to FIG. 2 , a plurality of openings or recesses 100 areformed in the conductive layer 90. The openings 100 are formed by anetching process, for example a dry etching process or a wet etchingprocess. The etchant is configured such that it will etch away theconductive layer 90 while leaving the etching-stop layer 80 mostlyintact, due to the high etching selectivity between the conductive layer90 and the etching-stop layer 80. The remaining portions of theconductive layer 90 may be referred to as conductive elements 90.

Referring now to FIG. 3 , a barrier layer 110 is formed over the topsurfaces and side surfaces of the conductive elements 90 (and overportions of the etching-stop layer 80 exposed by the openings 100). Thebarrier layer 110 is formed by a suitable deposition process and maycontain a dielectric material such as silicon nitride or siliconcarbide, etc.

Referring now to FIG. 4 , after the barrier layer 110 has been formed, atreatment process 130 is performed to treat the barrier layer 110. Insome embodiments, the treatment process 130 includes a plasma treatmentprocess using NH₃, O₂, He, Ar, N₂O, or CO₂. In some embodiments, thetreatment process 130 has a flow rate in a range from about 500 standardcubic centimeters per minute (sccm) to about 2000 sccm. In someembodiments, the treatment process 130 has a process temperature in arange from about 100 degrees Celsius to about 400 degrees Celsius. Insome embodiments, the treatment process 130 has a process pressure in arange from about 0.1 Torr to about 10 Torrs. In some embodiments, thetreatment process 130 has a process power in a range from about 50 Wattsto about 1500 Watts. In some embodiments, the treatment process 130 hasa process duration in a range from about 2 seconds to about 120 seconds.

The treatment process 130 changes the hydrophobicity of the surfaces ofthe barrier layer 110. In more detail, without being treated by thetreatment process 130, the surfaces of the barrier layer 110 aresomewhat hydrophobic. After being treated by the treatment process 130,the surfaces of the barrier layer 110 become hydrophilic. Experimentaldata has confirmed that the process conditions of the treatment process130 described above are configured to optimize the hydrophiliccharacteristics of the surfaces of the barrier layer 110. For example,in some embodiments, the hydrophilic surfaces of the barrier layer 110have a surface contact angle less than about 93 degrees, for example ina range from about 10 degrees to about 90 degrees. The hydrophilicproperty of the surfaces of the barrier layer 110 will help increase theporosity of a low-k dielectric material that will be formed in theopenings 100 in a later process, which will be discussed in more detailbelow.

Referring now to FIG. 5 , a low-k dielectric material 200 is formed overthe barrier layer 110. A low-k material refers to a dielectric materialwhose dielectric constant is less than the dielectric constant ofsilicon dioxide. As is shown in FIG. 5 , the low-k dielectric material200 fills the openings 100. In some embodiments, the low-k dielectricmaterial 200 is formed by a spin-on dielectric (SOD) coating process.The precursors for a polymer matrix of the low-k dielectric material 200include two components: a first component that does not containssilicon-methyl (Si-Me) and a second component that does contain theSi-Me. In some embodiments, the first component (that does not containSi-Me) contains Tetraethyl orthosilicate (TEOS) and Tetramethylorthosilicate (TMOS). TEOS has the following chemical formula:

TMOS has the following chemical formula:

In some embodiments, the second component (that does contain Si-Me)contains Triethoxymethylsilane (MTES) and Trimethoxymethylsilane (MTMS).MTES has the following chemical formula:

MTMS has the following chemical formula:

The chemical formulas for TEOS, TMOS, MTES, and MTMS are also shown inFIGS. 6A and 6B.

According to the various aspects of the present disclosure, the methylcontent (CH₃, or Me) can affect the properties of the resulting low-kdielectric material 200. As an example, the Si-Me content of theprecursor is correlated with (or affects) the resulting silicon-carbon(Si—C) area in the low-k dielectric material 200. The Si-Me content mayalso affect the hydrophobicity of the low-k dielectric material 200.Whereas conventional methods for forming a low-k dielectric material paylittle attention to the Si-Me content of the precursors, the presentdisclosure recognizes that it is beneficial to configure the Si-Mecontent to affect the properties of the low-k dielectric material 200,which will affect the formation of the porous structures as discussedlater.

In some embodiments, the Si-Me content is controlled by configuring themixing ratio (in terms of moles) of the second component (containsSi-Me) and the first component (no Si-Me) of the precursor. For example,the mixing ratio of the second component to the first component of theprecursor is configured to be in a range from about 0.1 to about 10according to various aspects of the present disclosure. In someembodiments, the mixing ratio of the second component to the firstcomponent of the precursor is configured to be in a range from about 0.3to about 3. These ranges are configured to optimize the materialproperties of the low-k dielectric material 200 to facilitate theformation of the porous structures in portions of the low-k dielectricmaterial within the openings 100. In some embodiments, the rangesdiscussed above for the mixing ratio may result in a Si—C area that islarger than about 8.3.

Referring back to FIG. 5 , the low-k dielectric material 200 contains aplurality of porogen molecules 210. According to the various aspects ofthe present disclosure, the porogens molecules 210 include surfactantsthat can form micelles (also referred to as micelle templates), whichare lipid molecules that arrange themselves in an approximatelyspherical form in aqueous solutions. To provide an example, FIG. 7illustrates a diagram of a micelle and a plurality of monomers thatcollectively make up the micelle according to an embodiment of thepresent disclosure.

A micelle contains both a hydrophobic region and a hydrophilic region.FIGS. 8A and 8B illustrate chemical formulas of two example embodimentsof a surfactant type porogen that can form the micelle template of FIG.6 . In FIG. 8A, the surfactant type porogen is a diblock co-polymer thathas a hydrophilic component and a hydrophobic component. In someembodiments, the hydrophilic component is polyethylene oxide (referredto as PEO), and the hydrophobic component is polypropylene oxide(referred to as PPO). In these embodiments, the diblock co-polymer hasthe following chemical formula (also shown in FIG. 8A):

In FIG. 8B, the surfactant type porogen is a triblock co-polymer thathas a first hydrophilic component, a hydrophobic component, and a secondhydrophilic component. In some embodiments, the first hydrophiliccomponent is PEO, the hydrophobic component is PPO, and the secondhydrophilic component is also PEO. In these embodiments, the triblockco-polymer has the following chemical formula (also shown in FIG. 8B):

Regardless of the embodiment, it is understood that the regions of themicelle (shown in FIG. 7 ) at or near the outside surface (i.e., thespherical surface) are hydrophilic according to the embodiments of thepresent disclosure.

Referring back to FIG. 5 again, the fact that the outer surfaces of themicelles are hydrophilic helps facilitate the movement of the porogens210 toward the openings 100, especially since the treated surface of thebarrier layer 110 are also hydrophilic. In other words, because themicelles in the porogens 210 have hydrophilic outer surfaces, they areattracted to the hydrophilic surfaces of the treated barrier layer 110.Thus, the porogens 210 inside the low-k dielectric material 200 get“sucked” into the openings 100 and will get “trapped” inside theopenings 100 due to the forces of surface attraction. As discussedabove, the carefully configured Si-Me content for the precursorcomponents also facilitates the movement of the porogens into theopenings 100. The low-k material 200 may have a hydrophobicity thateffectively “pushes” the porogens 210 downward into the openings 100.

It has been observed through experimental data that if the processconditions (e.g, 1. the treatment process 130 for making the barrierlayer 110 more hydrophilic, and 2. the mixing ratio for the matrixprecursor components to achieve a desired Si-Me content) are configuredcorrectly, a substantial majority of the porogens 210 will be “trapped”inside the openings 100. In some embodiments, almost all (e.g., greaterthan 99%) of the porogens 210 that are greater than a certain size willbe “trapped” inside the openings 100. The porogens that are not insidethe openings 100 may be significantly smaller, to the extent that theymay even appear invisible to an electronic inspection machine (e.g., aFourier Transform Infrared Spectroscopy (FTIR) machine). For example,the porogens 210 inside the openings 100 may have diameters that are inthe range of several nanometers, while the porogens outside the openings100 may have diameters that are in the range of several angstroms, whichmay lead to an overall size discrepancy of hundreds of times or eventhousands of times. For this reason and also for reasons of simplicity,any porogens disposed outside the openings 100 are not specificallyillustrated herein.

Referring now to FIG. 9 , a curing process 300 is performed to thesemiconductor device 50. The curing process 300 may be performed at ahigh temperature and may include an ultraviolet (UV) process or athermal process. In the UV curing process, the process temperature maybe in a range from about 350 degrees Celsius to about 450 degreesCelsius, and the process duration may last for about 3 minutes to about10 minutes. In the thermal curing process, the process temperature maybe in a range from about 350 degrees Celsius to about 450 degreesCelsius, and the process duration may last for about 30 minutes to about120 minutes.

The curing process 300 transforms the porogens 210 into porous elements310. For example, the micelles inside the porogens 210 are evaporated orotherwise removed by the curing process 300. As a result, a porousstructure (i.e., an empty or hollow space) is formed in place of each ofthe porogens 210. The porous elements 310 make the portions of the low-kdielectric filling the openings 100 even more low-k. This is because theair inside the porous elements has a dielectric constant is that isabout 1, which is lower than the dielectric constant of the low-kmaterial itself. In this manner, the overall dielectric constant of theportions of the low-k dielectric material 200 filling the openings 100is brought down by the presence of the porous elements 310.

Referring now to FIG. 10 , one or more via openings are formed over atleast some of the conductive elements 90. For example, a via opening 320is formed over one of the conductive elements 90. The via opening 320may be formed by an etching process, for example a wet etching processor a dry etching process. The via opening 320 may have an inversetrapezoidal shape in some embodiments, such that it is wider at the topand narrower at the bottom. This helps a conductive material to fill inthe opening 320 more easily in a subsequent process.

Referring now to FIG. 11 , a barrier layer 340 is formed inside the viaopening 320. In other words, the barrier layer 340 is formed on thesidewall surfaces of the opening 320 (sidewalls of the low-k dielectricmaterial 200) and over the portion of the barrier layer 110 above theconductive element 90. In some embodiments, the barrier layer 340 isformed by a suitable deposition process. In some embodiments, thebarrier layer 340 and the barrier layer 110 have the same materialcompositions and are formed by similar deposition processes. Thereafter,the portions of the barrier layers 340 and 110 disposed below the viaopening 320 are etched away, so that a portion of the conductive element90 is exposed by the via opening 320.

Referring now to FIG. 12 , a conductive via 360 is formed inside the viaopening 320. The conductive via 360 may be formed by a suitabledeposition process. The conductive via 360 may contain a metal material,for example copper, aluminum, tungsten, or combinations thereof. It isunderstood that the conductive via 360 and the conductive element 90 maybe formed as a part of a multi-layered interconnect structure. Forexample, the conductive elements 90 may be formed as the metal lines ina particular interconnect layer (e.g., Metal-0 or Metal-1) of theinterconnect structure, and the conductive via 360 provides electricalconnections between the conductive element 90 therebelow with otherelements (e.g., another metal line) in a different interconnect layer ofthe interconnect structure.

The low-k dielectric material 200 provides electrical insulation for thevarious conductive elements 90. The low-k dielectric material 200 may beconceptually divided into portions 200A and 200B, which are conceptuallyseparated by the broken lines illustrated in FIG. 12 . It is understoodthat there is no actual physical separation between the portions 200Aand 200B, and that the conceptual division herein is merely tofacilitate the ensuing discussions. The portions 200A are the segmentsof the low-k dielectric material 200 that fill the openings 100, whereasthe portion 200B are the segments of the low-k dielectric material 200that are disposed outside the openings 100 (and above the portion 200A).

As discussed above, due to the hydrophilic properties of the treatedsurfaces of the barrier layer 110 inside the openings 100 as well as thehydrophilic properties of the outer surfaces of the porogens 210 (shownin FIG. 5 ), the porogens 210 inside the low-k dielectric material 200are congregated inside the portion 200A of the low-k dielectric material200. The carefully configured mixing ratio of the Si-Me-containing andnon-Si-Me-containing precursors also result in properties of the low-kdielectric material that help push the porogens 210 downward into theportion 200A. As a result, following the curing process 300 thattransforms these porogens 210 into the porous elements 310, the porosityof the portion 200A of the low-k dielectric material 200 issubstantially greater than the porosity of the portion 200B of the low-kdielectric material 200. This is because of the high concentration ofthe porous elements 310 inside the portion 200A, while the porouselements disposed inside the portion 200B are significantly smaller insize (e.g., diameter differences of 5-10 times) and number. For thisreason and also for reasons of simplicity, the porous elements in theportion 200B are not specifically illustrated herein. In someembodiments, the portion 200A is at least 1.3 times to 3 times moreporous than the portion 200B. For example, the porosity of the portion200A is in a range from about 20% to about 30%, while the porosity ofthe portion 200B is in a range from about 10% to about 15%.

Also, since the porous elements 310 comprise mostly of air—which has alow dielectric constant of about 1—consequently the dielectric constantof the portion 200A of the low-k dielectric material 200 issubstantially lower than the dielectric constant of the portion 200B ofthe low-k dielectric material 200. In some embodiments, the dielectricconstant of the portion 200A is in a range from about 1.3 to about 2.3,while the dielectric constant of the portion 200B is in a range fromabout 2.3 to about 3.5. The lower value of the dielectric constant ofthe portion 200A is beneficial, since the portion 200A is the portionthat provides electrical isolation between the conductive elements 90.In this regard, the low-k material 200 is made to be even more “low-k.”Among other things, the lower value of the dielectric constant improvesan RxC performance.

As a corollary to the differences in porosity and dielectric constantbetween the portions 200A and 200B of the low-k dielectric material 200,the silicon content for these two portions 200A and 200B are alsodifferent. This is shown in FIG. 13 , which is a graph illustrating thesilicon content of an experimental sample. The graph has an X-axis and aY-axis. The X-axis represents depth or distance (measured from top tobottom), and the Y-axis represents the silicon content. A plot 400 isshown in FIG. 13 . The plot 400 represents the silicon content of thelow-k dielectric material 200 as it varies from the top (e.g., near theupper surface of the via 360) to the bottom of the openings 100.

Based on the plot 400, it can be seen that the silicon content of thelow-k dielectric layer is remain uniform throughout. In a segment 400Aof the plot 400, which represents the silicon content of approximatelythe portion 200A of the low-k dielectric material filling the openings100, the silicon content is low. This is another way of saying that theporosity of the portion 200A of the low-k dielectric material 200filling the openings 100 is high. Conversely, in a segment 400B of theplot 400, which represents the silicon content of approximately theportion 200B of the low-k dielectric material outside the openings 100,the silicon content is high. This is another way of saying that theporosity of the portion 200B of the low-k dielectric material 200disposed above the conductive elements 90 is low.

FIG. 14 is a flowchart of a method 500 of performing a semiconductorfabrication process according to various aspects of the presentdisclosure.

The method 500 includes a step 510 of forming a plurality of conductiveelements over the substrate. The conductive elements are separated fromone another by a plurality of openings.

The method 500 includes a step 520 of forming a barrier layer over theconductive elements. The barrier layer is formed to cover sidewalls ofthe openings.

The method 500 includes a step 530 of performing a treatment process tothe barrier layer. The barrier layer becomes hydrophilic after thetreatment process is performed. In some embodiments, the treatmentprocess comprises a plasma process using NH₃, O₂, He, Ar, N₂O, or CO₂.In some embodiments, the treatment process is performed under thefollowing process conditions: a flow rate in a range from about 500standard cubic centimeters per minute (sccm) to about 2000 sccm; aprocess temperature in a range from about 100 degrees Celsius to about400 degrees Celsius; a process pressure in a range from about 0.1 Torrto about 10 Torrs; a process power in a range from about 50 Watts toabout 1500 Watts; and a process duration in a range from about 2 secondsto about 120 seconds.

The method 500 includes a step 540 of forming a dielectric material overthe barrier layer after the treatment process has been performed. Thedielectric material may be a low-k dielectric material having adielectric constant lower than the dielectric constant of silicondioxide. The dielectric material fills the openings and contains aplurality of porogens. In some embodiments, the step 540 of forming thedielectric material comprises configuring a mixing ratio of amethyl-containing precursor component to a methyl-free precursorcomponent. In some embodiments, the forming of the dielectric materialis performed such that the porogens congregated inside the openings.

The method 500 includes a step 550 of curing the dielectric material.The porogens become porous after the curing.

It is understood that additional processes may be performed before,during, or after the steps 510-550 of the method 500 to complete thefabrication of the semiconductor device. For example, the method 500 mayinclude a step of forming a via opening over at least one of theconductive elements, and a step of forming a conductive via in the viaopening. For reasons of simplicity, additional fabrication steps are notdiscussed herein in detail.

Based on the above discussions, it can be seen that the presentdisclosure offers advantages over conventional methods and devices oflow-k dielectric material fabrication. It is understood, however, thatother embodiments may offer additional advantages, and not alladvantages are necessarily disclosed herein, and that no particularadvantage is required for all embodiments. One advantage is that thelow-k material of the present disclosure offers improved performance dueto the enhanced porosity. As discussed above, the surface treatment ofthe barrier layer to make it more hydrophilic attracts the porogens(also having hydrophilic outer surfaces) to be moved to inside theopenings 100 that separate the conductive elements. The carefullyconfigured mixing ratio of the matrix precursor components also resultin a material with properties that help push the porogens down towardthe openings. Consequently, after the curing process that transforms theporogens into the porous structures inside the low-k dielectricmaterial, the portions of the low-k dielectric material filling theopenings have substantially greater porosity than the portions of thelow-k dielectric material outside the openings. The greater porositycorresponds to a lower dielectric constant. Since the portions of thelow-k dielectric material inside the openings provide electricalisolation between the conductive elements, the lower dielectric constantis beneficial, for example it enhances the RxC performance.

Another advantage is that the present disclosure does not require manychanges to the existing method of fabrication. As such, it does notsignificantly increase fabrication cost, if at all.

One aspect of the present disclosure pertains to a semiconductor device.The semiconductor device includes a substrate and a plurality ofconductive elements disposed over the substrate. The conductive elementsare separated from one another by a plurality of openings. A dielectricmaterial is disposed over and between the conductive elements. Thedielectric material includes: a first portion that is disposed insidethe openings; and a second portion that is disposed over the openingsand over the conductive elements. The first portion is substantiallymore porous than the second portion.

Another aspect of the present disclosure pertains to a semiconductordevice. The semiconductor device includes a substrate and a plurality ofmetal elements disposed over the substrate. A low-k dielectric materialdisposed in between, and over, the metal elements. The low-k dielectricmaterial includes a first portion that is disposed between the metalelements. The first portion has a first dielectric constant. The low-kdielectric material includes a second portion that is disposed over themetal elements. The second portion has a second dielectric constant. Thefirst dielectric constant is lower than the second dielectric constant.The first dielectric constant and the second dielectric constant areeach less than a dielectric constant of silicon dioxide.

Yet another aspect of the present disclosure pertains to a method offabricating a semiconductor device. A plurality of conductive elementsis formed over the substrate. The conductive elements are separated fromone another by a plurality of openings. A barrier layer is formed overthe conductive elements. The barrier layer is formed to cover sidewallsof the openings. A treatment process is performed to the barrier layer.The barrier layer becomes hydrophilic after the treatment process isperformed. A dielectric material is formed over the barrier layer afterthe treatment process has been performed. The dielectric material fillsthe openings and contains a plurality of porogens.

The foregoing has outlined features of several embodiments so that thoseskilled in the art may better understand the detailed description thatfollows. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor device, comprising: a firstconductive element and a second conductive element each disposed over asubstrate; a first dielectric element disposed between the firstconductive element and the second conductive element, wherein the firstdielectric element contains a plurality of first porous components, andwherein a bottom surface of the first dielectric element is moreelevated vertically than bottom surfaces of the first conductive elementand the second conductive element; and a second dielectric elementdisposed over the first dielectric element and at least partially overthe first conductive element and over the second conductive element,wherein the first dielectric element and the second dielectric elementare different portions of a same continuous dielectric structure,wherein the second dielectric element contains a plurality of secondporous components, and wherein the second porous components are each atleast 5 to 10 times smaller in size than each of the first porouscomponents.
 2. The semiconductor device of claim 1, wherein the firstdielectric element has a substantially lower concentration of siliconthan the second dielectric element.
 3. The semiconductor device of claim1, wherein the first dielectric element is in direct physical contactwith the second dielectric element, and wherein the first dielectricelement and the second dielectric element each have a respectivedielectric constant that is lower than a dielectric constant of silicondioxide.
 4. The semiconductor device of claim 1, wherein a total numberof the first porous components located within the first dielectricelement is greater than a total number of the second porous componentslocated within the second dielectric element.
 5. The semiconductordevice of claim 1, further comprising: a hydrophilic liner thatseparates the first conductive element and the second conductive elementfrom the first dielectric element and the second dielectric element. 6.A semiconductor device, comprising: a plurality of conductive elementslocated over a substrate, wherein the plurality of conductive elementshave substantially co-planar bottom surfaces; a first porous dielectricstructure that surrounds each of the conductive elements laterally,wherein the first porous dielectric structure contains a plurality offirst porous elements; and a second porous dielectric structure that islocated directly over the first porous dielectric structure and is indirect physical contact with the first porous dielectric structure,wherein the second porous dielectric structure contains a plurality ofsecond porous elements that are smaller in size than the first porouselements by at least about 5 to 10 times.
 7. The semiconductor device ofclaim 6, wherein a total number of the first porous elements locatedwithin the first porous dielectric structure is greater than a totalnumber of the second porous elements located within the second porousdielectric structure.
 8. The semiconductor device of claim 6, furthercomprising: a hydrophilic layer located between the conductive elementsand the first porous dielectric structure.
 9. A semiconductor device,comprising: a first conductive component and a second conductivecomponent each disposed over a substrate, wherein the first conductivecomponent and the second conductive component have substantiallyco-planar bottom surfaces; a first dielectric component disposed betweenthe first conductive component and the second conductive component,wherein the first dielectric component contains a plurality of firstporous structures; and a second dielectric component disposed over thefirst dielectric component, wherein the first dielectric component andthe second dielectric component are component of a single continuousdielectric structure, wherein the second dielectric component contains aplurality of second porous structures that are each smaller in size thaneach of the first porous structures.
 10. The semiconductor device ofclaim 9, wherein: the first dielectric component has a first porosity;the second dielectric component has a second porosity; and the firstporosity is greater than the second porosity.
 11. The semiconductordevice of claim 10, wherein: the first porosity is in a range from about20% to about 30%; and the second porosity is in a range from about 10%to about 15%.
 12. The semiconductor device of claim 9, wherein thesecond porous structures are each smaller in size than each of the firstporous structures by about at least 5 to 10 times.
 13. The semiconductordevice of claim 9, wherein: a first number of the first porousstructures are disposed in the first dielectric component; a secondnumber of the second porous structures are disposed in the seconddielectric component; and the first number is greater than the secondnumber.
 14. The semiconductor device of claim 9, wherein: the firstdielectric component has a first dielectric constant; the seconddielectric component has a second dielectric constant; and the firstdielectric constant is lower than the second dielectric constant. 15.The semiconductor device of claim 14, wherein: the first dielectricconstant is in a range from about 1.3 to about 2.3; and the seconddielectric constant is in a range from about 2.3 to about 3.5.
 16. Thesemiconductor device of claim 9, further comprising a liner surroundingthe first dielectric component, wherein the liner has hydrophilicproperties.
 17. The semiconductor device of claim 16, wherein: firstportions of the liner are disposed on side surfaces and a bottom surfaceof the first dielectric component; and second portions of the liner aredisposed below a bottom surface of the second dielectric component. 18.The semiconductor device of claim 9, further comprising an etching stoplayer disposed below the first conductive component, the secondconductive component, and the first dielectric component, wherein theetching stop layer is in direct contact with the first conductivecomponent and the second conductive component.
 19. The semiconductordevice of claim 9, further comprising a third conductive componentdisposed over the first conductive component or the second conductivecomponent, wherein the second dielectric component surrounds the thirdconductive component laterally.
 20. The semiconductor device of claim 9,wherein each of the first porous structures or each of the second porousstructures consists of a hollow space.